1. Field of the Invention
The present invention relates to a clutch mechanism, particularly but not exclusively for automotive vehicles, of the kind comprising a pressure plate, elastic means such as a diaphragm spring and a cover.
2. Description of the Prior Art
The invention is more particularly concerned with means for limiting the travel of the pressure plate relative to the cover to prevent the drive tangs, constituting the rotational linkage between and permitting axial movement between the pressure plate and the cover the pressure plate and the cover, from tending to deteriorate when the pressure plate/diaphragm spring/cover combination is pre-assembled, but not yet bolted to the reaction plate. This situation occurs routinely, when pre-assembled units are kept in storage, for example.
The function of the tangs in question is not only to link the pressure plate elastically to the cover, but also to contribute to urging the pressure plate to the released position on releasing the clutch, to prevent the pressure plate rubbing on the friction disk. For this purpose, these tangs are treated to provide sufficient elastic return force.
When the pre-assembled combination is not bolted to the reaction plate, the pressure plate is urged strongly outwards by the diaphragm spring. As the only force to resist this is that provided by the tangs, these are also urged outwardly until equilibrium is established between the return force of the tangs and the force of the diaphragm spring. The tangs are therefore deformed and this distension may result in deterioration of their properties.
Deterioration may also occur, even if expansion of the diaphragm spring is limited, during careless handling, as when dropped, for example. By virtue of its non-negligible weight and its inertia, the pressure plate may move away from the cover to an extent sufficient to bring about significant deterioration of the properties of the tangs.
For this reason it is important to provide means for limiting the travel of the pressure plate.
Known limiting means include radial projections on the pressure plate and circumferential abutments on the cover. This involves relative rotation to bring the appropriate parts into axial alignment, after inserting the pressure plate into the cover.
Such arrangements are not convenient to use.
During assembly, it is not only necessary to insert the pressure plate into the cover (axial movement), but also to rotate the pressure plate so as to engage the projections opposite the abutments. Special-purpose assembly machines must therefore be provided to this end, able to sequence the necessary axial and then rotational movements.
This type of assembly results in relatively high production costs, arising out of the need for assembly benches as previously referred to and the associated assembly time.